Presently, there are two basic types of land-mobile communication systems: conventional communication systems (FIG. 1) and trunked communication systems (FIG. 2). Each type of communication system comprises a plurality of communication units, a limited number of communication resources, a communication resource allocator, and a plurality of operator stations (consoles). The communication resource allocator comprises a plurality of base interface modules (BIMs), a plurality of operator mux interface modules (OMIs), a plurality of audio expansion interface modules (AEIs), and at least one TDM bus. Each BIM acts as both a signal source and a signal destination. As a signal source, the BIM receives audio signals from at least some of the plurality of communication units, via a repeater or base station, converts the signals into digitized signals, and sources them to a slot in the TDM bus. See FIG. 3 for a typical TDM slot assignment pattern. (For an operational description of the TDM bus and slot location, refer to Motorola, Inc., Pub. No. R4-2-37C, CENTRACOM Series II Control Centers (March, 1988).) The BIM also acts as a designated signal source by conveying communication system data produced by a communication unit, or units, to the rest of the communication system. As a signal destination, the BIM receives digitized signals from the TDM bus, converts them to audio signals, and sends the audio signals to the repeater or base station such that the audio signals may be transmitted, via a communication resource, to at least some of the plurality of communication units.
Within either type of communication system, an OMI and an AEI are used to interface a console to the rest of the system. Generally, the OMI contains, in firmware, information that allows its respective console to perform supervisory functions and information regarding the typical communication system configuration. The typical communication system configuration includes, but is not limited to, the number of repeaters, number of signal sources, the number of signal destinations, the TDM slot assignments for each signal source and signal destination, the type of each BIM, and number and codes of communication groups. (For a detailed description of supervisory functions and CCMs, refer to Motorola, Inc. Pub. No. R4-2-73, CENTRACOM Series II Plus Control Centers (April, 1988). However, for use herein, consoles need not incorporate all of the described features as listed in the CENTRACOM Series II Plus Control Centers publication.) The OMI, as a designated signal source, sources communication system data to the TDM bus, wherein the communication system data comprises information about the typical communication system configuration, information about selected supervisory functions, and/or information about selected signal destinations. The OMI further acts as a signal source by receiving audio signals from its respective console, converting the signals into digitized signals, and sourcing the digitized signals, in the appropriate slot, to the TDM bus.
The OMI, however, does not act as a signal destination for its respective console, the AEI performs this function. The AEI, as a signal destination, receives digitized signals from the TDM bus, converts the signals into audio signals, and sends the audio signals to a speaker that is controlled by an assigned CCM of the console. The audio signals sent to the speaker may comprise a plurality of audio signals that were generated by several signal sources, such that the operator of the console may monitor and supervise several signal source via one speaker and one CCM per signal source. The AEI acts as a signal destination for each CCM on a console, thus if a console has ten CCMs, the AEI acts as ten signal destinations. It should be noted that the actual signal sources and signal destinations are the communication units and console, however, they are addressed by their respective communication system interfacing modules (BIMs, OMIs, and AEIs). Thus, for the purposes this discussion, the OMIs and BIMs will be referenced as signals sources, while the AEIs and BIMs will be referenced as signal destinations.
As described above, conventional communication systems and trunked communication systems have several characteristics alike, however, each communication system operates in a distinct mode. The typical conventional system of FIG. 1 comprises a plurality of communication units, a plurality of repeaters that transceive information via communication resources, a communication resource allocator (central electronics bank (CEB)), and a plurality of consoles. Also shown is a computer aided dispatcher (CAD) which may also be incorporated into trunked communication system. (For a description of the CAD, refer to Motorola, Inc. Pub. No. R4-2-73, CENTRACOM Series II Plus Control Centers (April, 1988).) The typical communication system configuration of a conventional communication system has communication groups assigned to specific repeaters, wherein specific consoles are assigned to monitor some of the communication groups. (A communication group comprises at least some of the plurality of communication units that are typically used for like purposes, e.g. police department, fire department, etc.) The repeater and communication group assignments may be changed by a CAD, but regardless of the assignments, a console monitors only the repeaters having at least one of its communication group assigned to it. For a further discussion of the convention system refer to U.S. Pat. No. 4,630,263, entitled TIME DIVISION MULTIPLEX COMMUNICATION CONTROL SYSTEM, assigned to Motorola, Inc.
The typical trunked communication system of FIG. 2 comprises a plurality of communication units, a plurality of repeaters that transceive signals via communication resources, a communication resource allocator, and a plurality of consoles. (As with a conventional communication system, the communication resources may be telephone lines, frequency pairs, carrier frequency, or TDM slots.) The typical communication system configuration of the trunked communication system comprises the communication units arranged into a plurality of communication groups, where the repeaters are allocated to a communication group upon request. The consoles are assigned to monitor specific communication groups, however, the console cannot monitor a specific repeater as in a conventional communication system. The console must receive information from the communication resource allocator about the repeater that has been allocated to one of its communication groups. For a further description of the trunked communication system refer to U.S. Pat. No. 4,698,805 entitled CONSOLE INTERFACE FOR A TRUNKED RADIO SYSTEM, assigned to Motorola, Inc.
Despite all the features that each communication system offers to subscribers (user of a communication unit) and console operators, their use is limited to the communication system that the subscribers and console operators are affiliated with. This may be a substantial limiting factor in large metropolitan areas having a large number of subscribers and console operators. For example, if a city has a large police force, fire department, and other civil service departments, several communication systems may be needed to adequately service them. Because communication systems may not actively communicate with other communication units, the city must have several central control stations instead of one. For example, if the city has thirty communication systems with the police force subscribing to several of the systems, the city's police force may not all communicate together, nor can one console operator send a supervisory message to the entire police force. Therefore, a need exists for a communication system network that allows communication units in either type of communication system to communicate with other communication units in the same or different communication systems and that allows console operators to monitor and supervise communication groups in its communication system as well as communication groups in other communication systems.